STL compatible iterators
Submitted by Gael Guennebaud @ggael
Assigned to Nobody
Link to original bugzilla bug (#231)
Version: 3.0
Description
Some day it would be cool to support STL's iterators, here is a start written by "inverse" from the forum (http://forum.kde.org/viewtopic.php?f=74&t=94120#p191501):
template<typename Value_t, typename Container_t>
class index_iterator : public std::iterator<std::random_access_iterator_tag, Value_t>
{
protected:
Container_t* container_;
int index_;
public:
index_iterator() : container_(0), index_(0) { }
index_iterator(Container_t& container, int index) : container_(&container), index_(index) { }
bool operator==(const index_iterator& other) { return container_ == other.container_ && index_ == other.index_; }
bool operator!=(const index_iterator& other) { return !(*this == other); }
Value_t& operator*() { return (container_)[index_]; }
Value_t const& operator() const { return (*container_)[index_]; }
Value_t* operator->() { return &((container_)[index_]); }
Value_t const operator->() const { return &((*container_)[index_]); }
index_iterator& operator++() { ++index_; return *this;}
index_iterator operator++(int) { index_iterator prev(*this); operator++(); return prev;}
index_iterator& operator--() { --index_; return *this;}
index_iterator operator--(int) { index_iterator prev(*this); operator--(); return prev;}
friend index_iterator operator+(const index_iterator& a, int b) { index_iterator ret(a); ret += b; return ret; }
friend index_iterator operator-(const index_iterator& a, int b) { index_iterator ret(a); ret -= b; return ret; }
friend index_iterator operator+(int a, const index_iterator& b) { index_iterator ret(b); ret += a; return ret; }
friend index_iterator operator-(int a, const index_iterator& b) { index_iterator ret(b); ret -= a; return ret; }
int operator-(const index_iterator& other) const { return index_ - other.index_; }
bool operator< (const index_iterator& other) { return container_ == other.container_ && index_ < other.index_; }
bool operator<=(const index_iterator& other) { return container_ == other.container_ && index_ <= other.index_; }
bool operator> (const index_iterator& other) { return container_ == other.container_ && index_ > other.index_; }
bool operator>=(const index_iterator& other) { return container_ == other.container_ && index_ >= other.index_; }
index_iterator& operator+=(int b) { index_ += b; }
index_iterator& operator-=(int b) { index_ -= b; }
Value_t& operator[](int i) { return (*container_)[i]; }
Value_t const& operator[](int i) const { return (*container_)[i]; }
};
template<typename Value_t, typename Container_t>
inline index_iterator<Value_t, Container_t> index_begin(Container_t& container)
{
return index_iterator<Value_t, Container_t>(container, 0);
}
template<typename Value_t, typename Container_t>
inline index_iterator<Value_t, Container_t> index_end(Container_t& container)
{
return index_iterator<Value_t, Container_t>(container, container.size());
}
template<typename Value_t, typename Container_t>
inline index_iterator<const Value_t, const Container_t> index_begin(const Container_t& container)
{
return index_iterator<const Value_t, const Container_t>(container, 0);
}
template<typename Value_t, typename Container_t>
inline index_iterator<const Value_t, const Container_t> index_end(const Container_t& container)
{
return index_iterator<const Value_t, const Container_t>(container, container.size());
}
usage example:
Eigen::MatrixXd m(100, 20);
auto row_2 = m.row(2);
auto begin = index_begin<double>(row_2);
auto end = index_end <double>(row_2);
// sort a row:
std::sort(begin, end);
// copy row to standard library container:
std::vector<double> std_v(begin, end);
// find a value in a row:
std::find(begin, end, 3.14);